1. Field of the Invention
This invention relates to a self-loading type of controlled deflection roll, such as used in the papermaking industry to provide at least one of a pair of nipped rolls to process a traveling web of paper. More particularly, this invention relates to a high temperature self-loading type of controlled deflection roll wherein the bearings on which the roll shell is rotatably mounted are shielded from the heat generated by the hydraulic fluid used to actuate one or more shoes within the roll to control the deflection of the roll shell. Still more particularly, this invention relates to a self-loading controlled deflection roll wherein the roll shell is pivotally mounted relative to the support shaft of the roll at either end of the roll at a point spaced outwardly from the end of the roll shell, and wherein the roll shell is supported on non-self-aligned bearings.
2. Description of the Prior Art
Controlled deflection rolls have been used in the papermaking industry for years to provide uniform nip loading between cooperating roll couples, at least one roll of which couple is such a controlled deflection roll, to process the paper web traveling in a papermaking machine. In the past few years, so-called self-loading controlled deflection rolls have been developed, particularly to be utilized in the press section of a papermaking machine, to provide roll loading, or nipping, engagement with a mating roll without the need for external arms to mount the roll and move it into and out of operating position. This saves considerable space and provides more flexibility in the design configuration.
As the speeds in papermaking machines have increased in order to provide a competitive paper product at competitive prices, the nip pressures required to dewater and otherwise process the ever-faster moving paper web have increased substantially. Further, the design of controlled deflection rolls has evolved into more sophisticated and versatile arrangements wherein the internal shoes which support and load the roll shell are individually controlled in both the axially and circumferentially extending directions relative to the internal surface of the roll shell. Such individual control includes different combinations of increased pressure over a greater segment of area of the internal surface of the roll shell, as well as greater pressures of the shoes against some segments of the annular inner surface area of the roll and lesser pressures against other inner surface areas of the roll shell. This has required the use of increased quantities of hydraulic fluid at increased pressures. Also, modern papermaking processes sometimes require a relatively high roll shell surface temperature. This, in turn, will result in the controlled deflection roll operating with its hydraulic fluid at a higher temperature. The temperatures of the hydraulic fluid used to actuate the shoes within the controlled deflection roll can reach about 400.degree. F. In some applications, such as press drying where the traveling paper web is pressed and partially dried at the same operation when it is nipped between two rolls, such temperatures are not altogether undesirable.
However, it has been found that there is no lubricant available for use in a hydrostatically loaded support shoe which can withstand temperatures above about 400.degree. F. for a prolonged period of time, such as is experienced in a papermaking machine which operates continuously for 24 hours a day, 7 days a week. In such applications, the lubricant possesses insufficient viscosity to properly maintain flow in order to lubricate the interface between the support shoe and the inner surface of the roll shell. In other words, the problem resides in providing sufficient pumping capacity, or otherwise maintaining sufficient lubricant flow at low viscosity.
Another problem resides in the fact that the ordinary ball or roller elements in bearings lose their hardness when operated at temperatures of about 400.degree. F. over a period of time. This greatly reduces their life and results in undesirable and costly downtime in a papermaking machine. Papermakers have indicated that they will require controlled deflection rolls in the future having operating parameters which will require lubricants to withstand temperatures of about 600.degree. F.
Various attempts to either solve or avoid the problem of providing adequate bearing lubrication while providing adequate viscosity to the roll shell deflection control support shoes have been promulgated in recent years, but no method has completely or adequately solved the problem, particularly while providing the desired operating flexibility desired by papermakers.
Thus, in Arav U.S. Pat. No. 4,821,384, a bearing-less design is disclosed which obviates the bearing softening problem by eliminating the bearings such that the rotating roll shell is supported and loaded into nipping engagement solely by a plurality of shoes disposed circumferentially about the support shaft. Other bearing-less designs for controlled deflection rolls have been devised, such as Crouse U.S. Pat. No. 4,852,229. The type of controlled deflection roll described in these patents has not yet been developed into a commercially acceptable product.
Other attempts to solve the problems associated with the break-down of the bearing lubricant in high-temperature controlled deflection rolls has involved the use of a liquid barrier seal between the interior cavity of the controlled deflection roll and the bearings rotatably supporting the roll shell. Such an arrangement is described in Pav et al U.S. Pat. No. 4,757,584.
To summarize the prior art, the bearings in a self-loading type of controlled deflection roll have either remained exposed to unacceptable high temperatures, or have been eliminated entirely, or the controlled deflection roll has not been able to be configured into the desired self-loading type of roll.